Conceptual Physics

Chapter 18 Problems

Conceptual Problems

C.1 The standard value for a healthy human's body temperature is 37°C, to the nearest Celsius degree, although this value is

only an approximation. In fact, the temperature of a healthy person varies by as much as 1.5°C each day, being lowest in the

morning and peaking in the evening. On North American fever thermometers, a "normal" body temperature is usually

indicated as 98.6°F. (a) Explain how this "normal" value in the Fahrenheit system is obtained from the "normal" value in the

Celsius system. (b) Explain why stating the value for a "normal" human temperature with three significant digits, as 98.6°F, is

misleading. (c) What would be a better "normal" value in the Fahrenheit system?

(a)

(b)

(c) °F

C.2 A new website comes out promoting the Cold Water Diet. It proclaims: "On the CWD, you eat all the carbs and fat you want,

and just drink cold water. One liter of cold water has a mass of 1000 g, and it takes 1.0 calorie to raise the temperature of 1.0

g of water by 1 Celsius degree. If you ingest a liter of water at 0°C, it will take 37,000 calories to raise the temperature up to

37°C, which is body temperature. That energy has to come from your body, so you can watch those pounds melt away!" What

is wrong with the website's claim?

C.3 A steel block is heated so that the length of each side increases 1%. What happens to its mass?

i. It increases 1%

ii. It increases 3%

iii. It increases 3.0301%

iv. It does not change

C.4 You want to use a calorimeter to measure the specific heat of a very small object that you suspect has a low specific heat

value. Assume that you can use any of three liquids to fill the calorimeter: water, ethyl alcohol (which has a specific heat of

2549 J/kg·K), or mercury (which has a specific heat of 139 J/kg·K). Which liquid would you choose, and why?

Water Ethyl alcohol Mercury

C.5 Why does a tiled floor feel colder to your bare feet than a carpeted floor, even though they are both at room temperature?

C.6 In coastal towns, breezes tend to blow offshore (from the land to the ocean) during the night and early morning, and onshore

(from the ocean to the land) during the afternoon and evening. What factors primarily contribute to this effect?

Heat conduction

Heat convection

Specific heat of land vs water

Salinity of the water

Thermal expansion

C.7 In outer space environments, such as on the International Space Station, why must every piece of machinery or electronic
equipment have its own cooling fan? This makes for a noisy environment. Hint: What is different compared to an Earth-based
laboratory, and why should this matter?

C.8 When people are extremely cold and are not prepared with warm clothing, they will sometimes crouch and curl up into a tight

roll, hugging their knees to their chests. How does such a position conserve body heat?

Section Problems

Section 2 - Temperature scales

2.1 Daniel Fahrenheit first proposed the temperature scale that bears his name in 1724. Originally, his reference points were a

well-mixed slurry melted from equal weights of ice and salt (similar to what you use in a hand-cranked ice cream freezer) for 0

degrees, and the temperature of the healthy human body for 12 degrees. Later he subdivided each one of his original

"degrees" into eight equal parts to define degrees Fahrenheit. In modern degrees Fahrenheit, what is the temperature of (a)

the ice-salt mixture? (b) Fahrenheit's "healthy human"?

(a) °F

(b) °F

Copyright 2007 Kinetic Books Co. Chapter 18 Problems^355